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nuckolls.bob(at)cox.net
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 Posted: Tue Sep 02, 2008 8:46 pm Post subject: Noise Filter for Strobe power and regulator? |
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At 07:50 AM 9/2/2008 -0600, you wrote:
| Quote: |
Bob and group,
Looks like Radio Shack has obsoleted both noise filters in Bob's related
article. Does anyone have a recommendation on either an appropriate
replacement noise filter or an appropriate choke (I've got appropriate
caps...) for use at a strobe power supply?
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Now does noise from the strobe manifest itself
in your system?
| Quote: | 2nd noise question: I'm planning on moving my "Ford Style" regulator up
into the nose of the longeze and adding an OVP module (with associated 5A
breaker). I'm assuming the regulator noise is field-current-loop noise
which implies it shouldn't change much (loop the same, position of
regulator is different). Is there other regulator based noise I should
worry about?
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No, these regulators have not proven to be
antagonists to other systems.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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steve(at)tomasara.com
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| Posted: Wed Sep 03, 2008 4:18 am Post subject: Noise Filter for Strobe power and regulator? |
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Bob,
Regarding my interest in a noise filter for my strobe:
| Quote: | **
Now does noise from the strobe manifest itself
in your system?
**
I was told it was audible via the intercom and the previous owner had
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glued (literally) a massive aluminum electrolytic to the top of the case
(the size of a tall drinking glass) "which helped" (as I remember being
told). I'm redoing the wiring from scratch and it's possible that
elimination of a previously existing big radio/intercom power feed loop
will have taken care of the problem but it seems prudent to put some
filtering in to replace the overly large cap.
My goal is to put in something "reasonable" and, with luck, not have
anything to chase down in this area when I power everything back up
again after the rewiring.
Steve Stearns
Boulder/Longmont, Colorado
CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)
Restoring (since 1/07): N45FC O235 Longeze Cothern/Friling CF1 (~1000 Hrs)
Flying (since 9/86): N43732 A65 Taylorcraft BC12D
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nuckolls.bob(at)cox.net
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| Posted: Thu Sep 04, 2008 9:42 am Post subject: Noise Filter for Strobe power and regulator? |
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| Quote: | >
> This is a LongEz? Where is the strobe supply mounted
> and how is it grounded? Do you have a single point
> ground system? Where are the microphone and headset
> jacks grounded?
>**
It's a LongEZ, I'm redoing the wiring (all of it..., In fact there is no
wire left in the airframe right now, but I made a full set of "as-builts"
before I ripped it all out) as I didn't like some things I found. The
first issue that I think could have been a big contributor for strobe
noise is that the power and ground for the radio and intercom stack (which
was one breaker for all, but will be separate fuses) ran different
directions from the radio with the ground running forward to the battery
while the power ran backward on the left side, crossed over to the right
side through the pilot headrest and then forward to the switch panel in
the right strake before continuing forward to the battery. This left a
huge inductive loop for noise pickup. This will be fixed. The strobe
power was mounted under the wing spar in the "hell hole" and was grounded
both directly to the firewall (via case mounting) and through a power
cable that ran up to the switch panel which there had a separate ground
back to the firewall. This put the the strobe in the middle of one of the
ground loops (all of which will be eliminated). The radio, intercom and
instruments, and this is worth something..., were at least on a separate
non-looped ground direct to the battery. At the jacks, the mic and
headphone jacks were only grounded to each other and to a ground wire and
the shields on a closely paired pair of shielded cables back to the
avionics harness. There was technically a ground loop in the two shields
but not an egregious one as there was no area within the loop (but it will
be fixed none-the-less).
From your questions I'm inferring that noise problems with a Whelen
Strobe supply is not a given. And I'm now expecting you might suggest
that since I'm rewiring and eliminating an obvious noise propagation path
(that from the nice open power supply ground-loop to the nice open radio
power path loop...) and possible other less-obvious ones (and hopefully
avoiding any of my own design) perhaps I should wait on the noise filter
until I determine if I still have a problem.
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There are tens of thousands of strobe systems flying
with no or (at least acceptably low) noise issues. So
yes, the need for filtering is not a given. Further,
the need to ADD filtering gives pause to wonder if
there are other deficiencies in the system integration
that drives the need for a band-aid filter later.
I've never had to "fix" a regulator installation
to mitigate a noise issue.
My suggestion is that you continue your clean-up
tasks with a goal of crafting a system that is as
tolerant of the strobe as the thousands of installations
cited above. After all, these ARE DO-160 qualified devices . . .
if they don't live happily in any given system, it's
likely that design deficiencies exist in the system.
The road to Nirvana starts at the common point ground
where electro-whizzies, battery(-) and a FATwire-to-
crankcase all come together. There can be other
ground wire concentration points but given the size
of this airplane and the narrow, tandem cockpit
width, the one-ground-does-it-all approach is doable
and attractive.
Lack of shielding (or inauspicious use of shielding)
is almost NEVER the source of a noise problem. Most of
our airplanes have much more shielded wire than is
necessary . . .
| Quote: | (In student mode...) How'd I do?
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The fact that you're sifting the sand with us
on such matters bodes well for success with
understanding.
Bob . . .
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